The present invention relates to an image-pickup apparatus such as a single-lens reflex camera including a shutter mechanism.
Some single-lens reflex digital cameras electrically control the charge accumulation time of an image-pickup element and employ a mechanical shutter to prevent unnecessary light from entering the image-pickup element (see Japanese Patent Laid-Open No. 2001-42386). The mechanical shutter in this case has shutter blades corresponding to a front curtain or a rear curtain of a typical focal-plane shutter.
Before image pickup, the shutter blades are closed to prevent unnecessary light from entering the image-pickup element. The shutter blades are opened in accordance with a release operation and an operation for so-called live-view display, for example. The shutter blades are again closed after image pickup. In such a mechanical shutter, the shutter blades are driven by a driving force from a spring, similarly to a typical focal-plane shutter. Thus, after image pickup, it is necessary to charge the spring in preparation for next image pickup.
Japanese Patent Laid-Open No. 2001-21944 has disclosed a focal-plane shutter called a double-light-shielding type. The shutter disclosed in Japanese Patent Laid-Open No. 2001-21944 is also called a direct-holding type. Specifically, a rear-curtain driving member for driving a rear curtain is held by an electromagnet in early stages of image-pickup operation, and when a charge lever (set member) is returned to the initial position, engagement of a rear-curtain operating member coupled to the rear curtain is released to open an aperture of the shutter. An electric current applied to the electromagnet is shut off in predetermined timing to drive the rear-curtain driving member biased by a charged spring together with the rear curtain, thereby shielding the aperture.
A single-lens reflex camera using an interchangeable lens has a problem of dust adhering to a surface of an image-pickup element to have an adverse effect in which the dust is taken in a picked-up image. To address this, Japanese Patent Application 2003-5254 has proposed a camera including a member (brush) attached to a shutter blade for cleaning a light-receiving surface of the image-pickup element.
The shutter disclosed in Japanese Patent Laid-Open No. 2001-42386 has only one pair of shutter blades, but it has a complicated structure and it is difficult to reduce the size.
It is possible to realize similar operations to those of the shutter mechanism in Japanese Patent Application 2001-42386 with a relatively simple configuration by using the rear-curtain driving mechanism in the focal-plane shutter disclosed in Japanese Patent Laid-Open No. 2001-21944.
When the configuration for cleaning dust adhering to the light-receiving surface of the image-pickup element is included in the shutter by providing the brush for the shutter blades as disclosed in Japanese Patent Application No. 2003-5254, the friction between the brush and the image-pickup element may affect shutter operation or reduce durability of the shutter. For this reason, it is preferable to use a movable member different from the shutter blades and to provide a brush on the movable member. However, when such a movable member (cleaning mechanism) is added to the shutter disclosed in Japanese Patent Application 2001-21944, the shutter and the camera on which the shutter is mounted are increased in size.